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Physics

Critical Angle Calculator

Find the incidence angle above which total internal reflection occurs.

SI units shown beside each fieldIdeal model explained below
Physics lab
Physics lab

Use the units beside each input and review the model assumptions.

See the method

Define your system

Runs on your device

Your calculated quantity

Your result

Let’s calculate.

Use the Calculate button to see your result.

Review the method below for assumptions and conventions.

How to use this tool

  1. Enter higher refractive index, lower refractive index.
  2. Select Calculate to view the result.
  3. Check the method and assumptions below before using the result.

The method, explained

Critical angle = asin(n2/n1), only for propagation from higher to lower index.

A WORKED EXAMPLE

Using higher refractive index = 1.5, lower refractive index = 1, the result is 41.8103149 degrees. Change these example inputs to match your task; use the method above to check each step.

Understanding your result

Measured from the normal. At the critical angle the ideal refracted ray runs along the interface.

What to keep in mind

Measured from the normal. At the critical angle the ideal refracted ray runs along the interface. An idealized educational model using the stated SI units. Real systems may need additional forces, losses or experimental measurements. Not a safety or equipment specification.

Common questions

How do I use this critical angle calculator?

Find the incidence angle above which total internal reflection occurs. Enter higher refractive index, lower refractive index. The starting example is editable; use values for the same system or project.

Which assumptions affect this result?

Measured from the normal. At the critical angle the ideal refracted ray runs along the interface.

Methodology maintained by ClarityKit. How these tools are built and checked.